1. Field of the Invention
The present invention relates to an image recording technique and, more specifically, to an ink jet printer which lends itself to use for double-side printing, and to the technique for controlling the ink jet printer.
2. Description of Related Art
An ink jet printer disclosed in Japanese Patent Laid-Open No. 9-254376 is known as a printer that is able to print images on both surfaces of a printing medium. When double-side printing mode is designated in this ink jet printer, a printing medium in the paper-feeding cassette is fed between a print head and a platen, passed therethrough, moved backward again, and then fed again between the print head and the platen from the same side. During such an automatic feeding operation, an image for the odd-numbered page is printed on one surface of the printing medium, and then an image for the even-numbered page is printed on the other surface of the printing medium (hereinafter, the surface on which the image for the odd-numbered page is printed is referred to as a front surface, and the surface on which the image for the even-numbered page is printed is referred to as a back surface of a printing medium).
In addition to this type of ink jet printer, as another type of printer that is able to print images on both surfaces of a printing medium, an ink jet printer in which the user reverses the printing medium which has finished printing on the front surface is also known. When double-side printing mode is designated in this type of ink jet printer, printing media are fed from the paper feeding tray successively, and images for the odd-numbered pages are printed on the front surfaces of these printing media. When all the images for the odd-numbered pages were printed, the user reverses a stack of printing paper on which the images for odd-numbered pages are printed and loads it again on the paper feeding tray, so that those printing medias are again fed from the paper feeding tray successively, and the images for the even-numbered pages are printed on the back surface thereof successively.
In these two types of ink jet printers, positioning of the leading edge of the printing medium being conveyed with respect to the print head is carried out by suspending the rotation of the upper and lower registering rollers arranged before the print head and abutting the leading edge of the printing paper against the nip between those registering rollers. This type of registering roller is stated in Japanese Patent Laid-Open No. 5-147208 relating to the ink jet printer that is able to print on both surfaces of a printing medium.
In general, the condition of the printing medium of the printing paper is apparently different before and after the page image is printed on the front surface as shown below. Since the printing medium having printed the page image on the front surface contains ink therein, the weight is increased in comparison with the blank printing medium including no ink at all as a matter of course. In addition, the printing medium having printed a page image on the front surface is subject to irregular waves or curls. In this way, the printing medium of which increased in weight corresponding to the weight of ink, or the printing paper having irregular waves or curls may not be able to travel smoothly when it is fed in the same condition as the case of the blank printing medium. It may cause skew. Since the printing medium having a page image printed on the front surface thereof contains ink therein and thus the hygroscopicity is deteriorated, it needs longer time to be dried than the blank printing medium. Therefore, when the page image is printed again on the back surface of the printing medium that is deteriorated in hygroscopicity, the image cannot be dried in a short time as in the case of the blank printing medium.
However, in the two types of ink jet printers described above, the printing medium is fed in the same way for the front surface printing and the back surface printing. Therefore, when printing the image on the back surface, the medium cannot be fed as smoothly as the case of printing on the front surface. Therefore, when printing the page image on the back surface of the printing medium, the upper and lower registering rollers may start rotating again before the whole portion of the leading edge of the printing medium abuts completely against the nip between the upper and lower registering rollers. When it happens, the printing paper is conveyed from between the upper and lower registering rollers toward the print head even though the alignment of the leading edge of the printing medium with respect to the print head is not correctly made. When printing of the page image on the back surface is started under such a condition, the page image cannot be printed at the correct area on the back surface of the printing medium. Consequently, there may be the case where the page images printed on both surfaces of the printing medium are not in parallel with respect to each other. In the case of double-side printing for three or more pages, there may be the case where the printed printing medias are stacked one on another on the paper receiving tray even though ink on the back surface is not completely dried. When it happens, ink on the back surface of each printing medium on the paper receiving tray is transferred to the front surface of another printing medium, thereby deteriorating the quality of the page image for both surfaces of each printing medium on the paper receiving tray. It is apt to happen especially when the photo image is printed on the back surface.
The double-side printing function as described above is not inevitable for printing the page image on both surfaces of the printing medium. As stated in Japanese Patent Laid-Open No. 5-147208, for example, the existing ink jet printer that has no double-side printing function may also be used for printing the page image on both surfaces of the printing medium if the user deliberately carries out two steps of; giving an order to print only the images for the odd-numbered pages in the first place, and then designating to print only the images for the even-numbered pages. However, it is troublesome for users because it requires the repeated operations that are not necessary in the normal one-side printing.
Other techniques relating the printer that is able to print on both side surfaces of the printing medium are shown in Japanese Patent Laid-Open No. 3-100760, No. 4-49069, No. 63-236653, No. 1-299078, No. 63-3986, No. 2-14175, No. 11-99724, No. 11-227278, No. 6-344606, and U.S. Pat. No. 2,839,334.